People with tuberculosis, especially those who also have diabetes, often have low vitamin D levels. Their bodies show higher levels of the antimicrobial peptide LL‑37 and certain immune signals (IFN‑γ, IL‑4, IL‑17), likely as a response to the infection. The study suggests that giving vitamin D could help these patients, and that LL‑37 and the immune signals might serve as markers of disease activity.

Pulmonary tuberculosis (PTB) is a high burden infectious disease in China. The immune function is damaged in patients with diabetes mellitus (DM) who are easy to infect with <i>Mycobacterium tuberculosis</i> (Mtb). The growth of Mtb has been shown to be restrained following the administration of vitamin D and antimicrobial peptide cathelicidin (LL-37); however, the effect in patients with DM and PTB remains unclear. Vitamin D can regulate the immune system through Vitamin D receptors expressed in T helper (Th) cells. The aim of the present study was to analyze the status and correlations of vitamin D, LL-37 and Th-associated cytokines in patients with PTB or PTB with DM (DMPTB). Serum 25-hydroxyvitamin D₃ [25(OH)D₃] levels were measured by liquid chromatography-tandem mass spectrometry, while plasma LL-37 levels were analyzed using a solid-phase enzyme-linked immunosorbent assay. Flow cytometry was used to analyze the levels of Th cytokines, including Th1-associated IFN-&#x3b3;, Th2-associated IL-4 and Th17-associated IL-17. The results revealed that patients with PTB and DMPTB were vitamin D deficient or had insufficient vitamin D levels. Furthermore, the levels of LL-37, IFN-&#x3b3;, IL-4 and IL-17 were higher in the PTB and DMPTB groups when compared with the normal controls. These results indicated that vitamin D supplementation is necessary for PTB and DMPTB patients. In addition, LL-37, IFN-&#x3b3; and IL-17 may be diagnostic indexes that become elevated in the compensatory response caused by Mtb infection. Vitamin D can regulate the immune status in patients suffering from PTB.